title: Comparison between bispectral index and patient state index as measures of the electroencephalographic effects of sevoflurane.
abstract: BACKGROUND
  The Bispectral Index (BIS) and the Patient State Index (PSI) quantify depth of anesthesia by analyzing the electroencephalogram. The authors examined the response of BIS and PSI to sevoflurane anesthesia.
  
  
  METHODS
  In 22 patients, sevoflurane anesthesia was induced by inhalation with a tight-fitting facemask and was maintained via a laryngeal mask. Sevoflurane concentrations were increased until burst suppression occurred and subsequently decreased until BIS recovered to values above 60. This procedure was repeated twice until patients underwent intubation for subsequent surgery. End-tidal sevoflurane concentrations, BIS, and PSI were recorded simultaneously. The performance of PSI and BIS to predict the estimated sevoflurane effect site concentration, as derived from simultaneous pharmacokinetic and pharmacodynamic modeling, was compared by determination coefficients (rho(2)) and prediction probabilities (P(K)).
  
  
  RESULTS
  A significant (P < 0.001) correlation between BIS and PSI was found (r(2) = 0.75), and a close sigmoid relation between sevoflurane effect site concentration and both BIS (rho(2) = 0.84 +/- 0.09) and PSI (rho(2) = 0.85 +/- 0.15) was observed. The maximum sevoflurane electroencephalographic effect resulted in PSI values (1.3 +/- 4.3) that were significantly (P = 0.019) lower than BIS values (7.9 +/- 12.1), and the effect site efflux constant k(e0) was significantly smaller (P = 0.001) for PSI (0.13 +/- 0.08 min(-1)) than for BIS (0.24 +/- 0.15 min(-1)). The probability of BIS (P(K) = 0.80 +/- 0.11) to predict sevoflurane effect site concentration did not differ (P = 0.76) from that of PSI (P(K) = 0.79 +/- 0.09).
  
  
  CONCLUSIONS
  The BIS reacted faster to changes in sevoflurane concentrations, whereas the PSI made better use of the predefined index range. However, despite major differences in their algorithms and minor differences in their dose-response relations, both PSI and BIS predicted depth of sevoflurane anesthesia equally well.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany. martin.soehle@ukb.uni-bonn.de
authors.forename: Martin
authors.initials: M
authors.lastname: Soehle
authors.forename: Richard K
authors.initials: RK
authors.lastname: Ellerkmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Grube
authors.forename: Matthias
authors.initials: M
authors.lastname: Kuech
authors.forename: Stefan
authors.initials: S
authors.lastname: Wirz
authors.forename: Andreas
authors.initials: A
authors.lastname: Hoeft
authors.forename: Joergen
authors.initials: J
authors.lastname: Bruhn
mesh_terms: D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects* / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D012107:Research Design; D000077149:Sevoflurane; D013997:Time Factors
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane